It is known that ethyl-1-ethyl-6-fluoro-7-chloro-4-oxo-1,4-dihydro-quinoline-3-carboxylate (Journal of Medicinal Chemistry 23, 1358 (1980); Japanese patent specification No. 80 33,453) is an intermediate useful in the preparation of 1-ethyl-6-fluoro-7-substituted-4-oxo-1,4-dihydro-quinoline-3-carboxylic acids having antibacterial effect (Ann. Microbiol, Paris 1981, 132A, 267; Journal of Medicinal Chemistry 1980, 23, 1358; Pathol. Biol. 1982, 30, 394; Cyo Yakuri, 1983, 25, 475; Pathol. Biol. 1983, 31, 501; Antimicrob. Agents Chemother. 1980, 17, 103; 1981, 19, 188; 1981, 20, 265; C. R. Scances Acad. Sci., Ser. 3, 1981, 292, 37).
The latter compounds can be prepared in two steps by reacting ethyl-1-ethyl-6-fluoro-7-chloro-4-oxo-1,4-dihydro-quinoline-3-carboxylate with a cyclic amine at a temperature above 100.degree. C. in the presence of a solvent for several hours and subjecting the ethyl-1-ethyl-6-fluoro-7-substituted-4-oxo-1,4-dihydro-quinoline-3-carboxy late thus obtained to hydrolysis; the order of succession of the said two steps can be changed, if desired (Japanese patent specification Nos. 79,138,582 and 80,33,453; Belgian patent specification Nos. 863,429; 870,917; 879,106 and 890,223; DOS No. 2,840,910 and French patent publication No. 2,424,919).
The above processes are accompanied by several drawbacks. The reaction time used is long. Moreover the halogen/amine group replacement reaction is not selective and in addition to the desired chloro/amine reaction in position 7 also a fluoro/amine exchange in position 6 takes place to a considerable extent.